1. Field of the Invention
The present invention relates to semiconductor processsing tools and, more particularly, to a method and apparatus for scheduling the movement of a semiconductor object through a processing tool.
2. Prior Art
Scheduling a semiconductor object processing tool, such as a cluster tool, involves specifying a sequence of transport mechanism actions and their times, as applied to the objects, and moving the objects between processing modules while satisfying timing and throughput requirements. Due to stringent timing and throughput requirements, the scheduling problem in these tools can be quite complex.
U.S. Pat. No. 5,801,945 discloses a scheduling method for a robotic manufacturing process. The method includes adjusting a timetable so that the last operation to occur to an object is planned to occur as soon as possible and the first operation for the object is planned to occur as late as possible.
The present invention is directed to, in a first aspect, a method for scheduling the allocation of resources in a semiconductor processing tool. The method generally comprises identifying a conflict in a resource allocation schedule for the processing of semiconductor objects through the tool over time. Preferably, the schedule utilizes a fundamental period for scheduling the periodic introduction of the objects into the tool for processing. Conflicts occur when a transport mechanism adapted to move the objects to and from the resources in the tool is scheduled to execute more than one transport action in a given time interval. Time blocks in the schedule for the resources are rescheduled from a present time interval to a different time interval. Preferably, the rescheduling of a time block does not violate a post-processing residency constraint for a residency time that the object spends in the resource whose time block is rescheduled.
In another aspect, the present invention is directed to a method for resolving a conflict in an object processing tool resource allocation schedule. The total time of the initial schedule is increased, without changing the fundamental period of the schedule until all conflicts in the schedule are resolved. The total time of the initial schedule is increased by moving a transport action associated with the conflict to start at an earlier time slot to form a target schedule. The moving of the transport action does not violate a post-processing residency constraint for a residency time that the object spends in the resource whose transport action is moved. The total time is increased until all conflicts are resolved or until a bound on increasing the total time of the schedule is reached.
In yet another aspect, the present invention is directed to a computer program product. The computer program product comprises a computer useable medium having computer readable program code means embodied therein for causing a computer to resolve a conflict in a schedule for a semiconductor object processing tool. The computer readable program code means in the computer program product comprises computer readable program code means for causing a computer to reschedule at least one time block in the schedule from a present time interval to a different time interval. The rescheduling of the time block does not violate a post-processing residency constraint for a residency time that the object spends in the resource whose time block is rescheduled.